A 2-day-old neonate has cyanosis that does not improve with 100% oxygen administration (hyperoxia test: PaO2 increases from 40 to only 48 mmHg). Cardiac impulse is in the midline and heart sounds are best heard on the right. Echo confirms dextrocardia with situs inversus. The most likely underlying structural defect in the setting of cyanosis unresponsive to oxygen is:

• A Tetralogy of Fallot
• B Critical pulmonary stenosis
• C Transposition of the great arteries ✓
• D Total anomalous pulmonary venous connection

Explanation

A hyperoxia test PaO2 that fails to exceed 150 mmHg (or rise significantly above 50 mmHg) indicates obligate intracardiac mixing, pointing to transposition of the great arteries (TGA) or TAPVC. TGA is the commonest cyanotic CHD presenting in the first 24–48 hours with profound cyanosis and poor response to oxygen. Tetralogy of Fallot typically presents later and shows better oxygen response due to variable right-to-left shunt. TAPVC is also a consideration, but TGA is the classic neonatal presentation here.

Reference: Ghai Essential Pediatrics, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.